The applicants have demonstrated an unusual association of apparently unrelated hematological abnormalities in a group of HIV-l infected individuals. HIV-l seropositive, thrombocytopenic individuals showed marked alterations in their B-cell subsets. Although B-cell numbers were normal, both the proportion of CD5+ cells and their absolute number were increased and the absolute number of CD5- B-cells were markedly reduced. In some patients 90 percent of the circulating B-cells were CD5+ (normal=18.2 + 2.3%). The alteration in the B-cell subsets was neither attributable to changes in CD4 or CD8 cell number, CD4/CD8 ratio, or absolute lymphocyte count nor to severity of disease nor to AZT treatment. The applicants suggest that it is improbable that the association of thrombocytopenia and aberrant B-cell profile occurred through happenstance. Their proposal is designed to investigate the basis of the association. Three possible explanations will be examined: (1) Both the abnormalities could be consequences of an autoimmune response, associated with the prevalence of CD5+ B cells, and directed against either the mature cells or their progenitors in the marrow. Sera from infected patients will be assayed for autoantibodies reactive with B cells and platelets or their progenitors. The applicants will also seek cell-bound autoantibodies or immune complexes similar to those found on platelets of patients with HIV-1 + ITP. If anti-B-cell antibodies are found, they will determine how CD5+ B-cells escape this autoimmune response. (2) The abnormalities could be a direct effect of HIV-l infection on either a hematopoietic precursor or a cell necessary for the development of B-cells and megakaryocytes. Both long term bone marrow cell cultures and short-term clonal cultures will be used to study the effects of virus, HIV-l infected cells and serum on the development of B-cells. (3) The changes in lympho-hematopoiesis could be a result of dysregulation induced by either the deficiency of CD4+ T- cells or the excess of CD8+ T-cells. T-cell derived cytokines are known to have profound effects on both MK and B-cell development. The relative T-independence of the CD5+ subset may account for their persistence. This possibility will be examined using two model systems. In the first, selected populations of human cells from uninfected subjects will be transferred to immunodeficient (SCID) mice. Cell sorting will be used to isolate highly enriched populations of CD5+ and CD5- B-cells, or their precursors as well as T-cell populations expressing either CD4 or CD8. Various combinations of these populations will be injected and the survival of the B-cell subsets determined. In the second model, an attempt will be made to reproduce the phenomenon in a totally murine system. Again, cells of the necessary phenotypes will be prepared by cell sorting and injected into SCID mice, but in this model only cells from syngeneic mice will be transferred, eliminating the possibility that problems of histo-incompatibility will confound the developmental studies.